1. Field of the Invention
The present invention relates to a method for making yoghurt and, more particularly, to a method for preparing sterile yoghurt which is capable of stable storage for six months without refrigeration.
2. Description of the Prior Art
It is generally well known that yoghurt is a product formed from milk which has been heated, cultured with a yoghurt culture such as Lactobacillus bulgaricus and Streptococcus thermophilus, incubated at about 40.degree.-45.degree. C. for a time sufficient to reach an acidic pH of 3.5 to 5.0, refrigerated to stop the growth of microorganisms, and then packaged for sale. Depending upon the consistency and flavor desired, various sweetners, stabilizers, fruits or other aromatic substances have been added to the yoghurt product prior to packaging. However, yoghurt produced according to conventional processes requires refrigeration during storage and/or transportation until immediately prior to consumption to prevent the growth of bacteria and/or the formation of mildew or other decomposition products.
In order to overcome the logistical inconvenience and expense incident to continuous refrigeration up until consumption, it has been an object of yoghurt manufacturers to prepare, if possible, a sterile form of the product which is not subject to deterioration in so rapid a manner as is characteristic of the conventionally prepared product. U.S. Pat. No. 3,932,680 assigned to the same assignee as the present invention suggests one way of achieving this result. According to the yoghurt preparation process taught in that patent, a sterile yoghurt can be prepared as follows:
(a) pasteurizing milk at a temperature of at least 90.degree. C. and homogenizing the milk; PA1 (b) concentrating the pasteurized and homogenized milk by 10% by weight at a temperature of about 92.degree. C.; PA1 (c) adding 10%-12% by weight sugar to the concentrated milk; PA1 (d) cooling the sugar-containing milk to about 40.degree. C.; PA1 (e) adding lactic acid bacterial cultures and incubating to pH 4-4.3 over 21/2-hours at 42.degree.-44.degree. C.; PA1 (f) cooling the acidified milk (yoghurt) to 20.degree.-30.degree. C.; PA1 (g) cooling the yoghurt to 4.degree.-12.degree. C.; PA1 (h) adding an effective amount of a stabilizer A containing, by weight, 20-30% emulsifier, 30-40% carageen, 30-40% carboxymethylcellulose, 2-3% carob-bean meal or powder and 4-8% guar meal or powder; PA1 (i) adding an effective amount of a stabilizer B which is potato or other starch; PA1 (j) adding an effective amount of a stabilizer C containing, by weight, 75-85% pure modified plant starch and 15-25% of 60% modified gelatin and sucrose wherein the sucrose is the carrier; PA1 (k) permitting the resulting mass to stand at 4.degree.-12.degree. C. for 5-7 hours; PA1 (l) filling the mass into packages and hermetically sealing same; PA1 (m) sterilizing the packages in an autoclave at temperatures in the range 60.degree.-85.degree. C. and at a pressure up to 2 atmospheres for a time sufficient to sterilize; PA1 (n) cooling the packages under pressure to 10.degree.-15.degree. C.; PA1 (o) storing the cooled packages for 2-4 days at 4.degree.-6.degree. C.; and PA1 (p) storing the packages at room temperature. PA1 20-30% by weight emulsifier (GMS-33 glycerin monostearate) PA1 30-40% by weight carageenan (Satiagel HV ex rot 5270) PA1 30-40% by weight carboxymethylcellulose (AKU-CMC 4 F 850) PA1 2-3% by weight carob-bean meal or powder (Poly-gum 14 T) PA1 4-8% by weight guar meal or powder (Polygum 26 N) PA1 Potato Starch PA1 75-85% by weight SuCrest YO-72 (pure modified plant starch) PA1 15-25% by weight SuCrest YO-100 (60 percent modified gelatin and sucrose wherein the sucrose is the carrier) PA1 (a) 10-15 days at 30.degree.-37.degree. C.; PA1 (b) 5 days at 50.degree. C.; PA1 (c) 90 days at 20.degree.-30.degree. C.; PA1 (d) 120 days at 15.degree.-25.degree. C.; PA1 (e) 240 days at 4.degree. C.;
Although good results have been obtained using the foregoing method of U.S. Pat. No. 3,932,680 it is now believed that a still better sterile yoghurt product having improved shelf stability can be prepared.